An AC-type gas-discharge display device is a large-sized/large capacity flat display and is also used as a household wall-mounted television. AC-type gas-discharge display devices include a two-electrode type and a three-electrode type, various systems such as an address/display non-separation system in which a period during which a cell to be displayed is defined (address period) and a display period (sustain period) during which a discharge is caused to occur to display and light the cell are shifted sequentially, and an address/display separation system in which those periods are separated. The present invention is applied to a three-electrode type AC-type gas-discharge display device, PDP device, of the address/display separation system as an example of the PDP devices.
In a three-electrode AC-type plasma display panel, a front glass substrate, which is a display screen, and a back glass substrate are arranged in opposition to each other with a discharge space sandwiched in between, a plurality of first (X) electrodes and a plurality of second (Y) electrodes are arranged by turns so as to make pairs on the front glass substrate, and the surface is covered with a dielectric layer. On the back glass substrate, a plurality of third (address) electrodes are provided so as to intersect the X and Y electrodes at right angles and a noble gas is sealed in the discharge space. On the address electrode, a phosphor layer, that emits light due to ultraviolet radiation generated by a discharge, is provided. A cell is formed at the intersection of a combination of the X electrode and the Y electrode that makes a pair and the address electrode. Ribs are provided between the address electrodes and the cells are separated into columns.
A PDP device is constituted by a plasma display panel, drive circuits for driving various electrodes provided on the plasma display panel, a control circuit for controlling the drive circuits, etc. A plasma display panel is capable of only providing lit or unlit states and therefore a gradated display cannot be provided. Because of this, a PDP device provides a gradated display by constituting one display frame by a plurality of subframes and combining the subframes to be lit. Each subframe is constituted by a reset period during which all cells are brought into a uniform state, an address period during which cells (display cells) to be displayed (lit) are selected, and a sustain discharge period during which the selected display cells are lit. In a general drive method, during the reset period, a high voltage is applied between all the X electrodes and Y electrodes and between all the address electrodes and the Y electrodes to cause a reset discharge to occur on the entire surface of the panel, whereby all the cells are brought into a uniform state. During the address period, a scan pulse is applied sequentially to the Y electrode and, in synchronization with the application of the scan pulse, an address pulse is applied to the address electrode of the display cell to cause an address discharge to occur in the display cell. Wall charges are formed in the cell in which the address discharge has occurred. During the sustain discharge period, a sustain pulse is applied alternately between all the X electrodes and the Y electrodes. Due to this, sustain discharge voltages of opposite polarities are applied alternately between the X electrodes and the Y electrodes and in the display cell, the voltage due to the wall charges formed by the address discharge is added and a sustain discharge is caused to occur, however, in the non-display cell, wall charges are not formed and therefore a discharge is not caused to occur by the sustain discharge voltage. The number of times of the sustain pulse is set for each subframe and the luminance of the subframe is determined by the number of times of the sustain discharge.
The conventional PDP device is explained as above. However, the PDP device is described in patent documents 1 to 3 etc. and, therefore, a more detailed explanation is omitted here.
A PDP device is required to have a display quality and a cost at the same level as those of a CRT. As mentioned above, during the sustain discharge period, the sustain pulse is applied repeatedly between all the X electrodes and the Y electrodes and the sustain discharge is caused to occur on the entire surface and therefore, the peak current of the sustain discharge becomes very large. In particular, the larger the current is, the more the luminance/light emission can be improved. Because of this, it is necessary for the drive circuit that supplies the X electrode and the Y electrode with the sustain pulse to be capable of supplying such a large current at high speed and, therefore, there arises a problem that the cost is increased. Further, if a large current flows, the voltage drop due to the resistance of the electrode and the wire becomes large and the voltage to be supplied differs depending on the position of the cell and, therefore, there arises a problem that the luminance is reduced partially and the operating margin is reduced. In particular, the reduction in luminance produces unevenness an streaking and degrades the display quality because of luminance changes between a row (display) line with many display cells and a row line with few display cells.
Consequently, it has been suggested to reduce the peak current of the sustain discharge. It is known that if the frequency of the sustain discharge is increased, the luminance can be increased and, in accordance with this, the discharge current can be reduced. However, if the drive frequency of the drive circuit is increased, the power loss is increased and there arises a problem that the cost of the circuit is raised and further, there arises another problem of the limit of the operation frequency for stably performing the operation of the sustain discharge. Because of this, at present, it is difficult to further increase the frequency of the sustain discharge.
On the contrary, it has been suggested to reduce the peak current by lengthening the intervals of the sustain discharges, that is, by making the rise of the sustain discharge more gradual, however, this method will reduce the number of times of the sustain discharge during the sustain discharge period and degrade the luminance and therefore, the method cannot be used.
Patent document 1 describes a configuration, in which the pairs of the X electrode and the Y electrode are divided into a plurality of groups and, by shifting the application timing of the sustain pulse to cause the sustain discharge to occur at different timings, the peak current of the sustain discharge is reduced. However, with the configuration described in patent document 1, there is a problem that, as one period of the sustain discharge is increased substantially, it is difficult to realize a high-frequency drive and a high luminance for the above-mentioned reason. Further, with the configuration described in patent document 1, a pair of the X and Y electrodes charges and discharge the inter-electrode capacitance between the pair and the Y electrode of a neighboring pair and between the pair and the X electrode of the other neighboring pair and, therefore, there arises a problem that power consumption is increased.
In patent document 2, a configuration is described in which the address electrodes are divided into two groups, and to the address electrodes of one of the groups, a discharge promotion pulse, which is synchronized with the sustain pulse and which is earlier and narrower than the rise of the sustain pulse, is applied, and to the address electrodes of the other group, a fixed voltage is applied, whereby a trigger discharge is caused to occur in the display cell of the address electrode of the one of the groups. Due to this, in the display cell of the address electrode of the one of the groups, the sustain discharge is caused to occur earlier than the sustain discharge in the display cell of the address electrode of the other group and, thereby, the peak current of the sustain discharge is reduced.
However, with the configuration described in patent document 2, it cannot be said that the wall charges are utilized sufficiently when the discharge promotion pulse is applied to the address electrode to cause a discharge to occur and therefore, it is necessary to raise the voltage of the discharge promotion pulse in order to obtain a sufficient effect of the trigger discharge and there arises a problem that power consumption is increased. Further, there is a problem that the power consumption is large because both the rise and the fall of the discharge promotion pulse are shifted from the rise and fall timing of the sustain pulse.
Patent document 3 describes a configuration in which the pulse is applied alternately to odd-numbered address electrodes and even-numbered address electrodes in synchronization with the sustain pulse, whereby the occurrence of the sustain discharge is shifted and thus the peak current is reduced.
However, with the configuration described in patent document 3, the pulse is applied to the odd-numbered address electrodes and the even-numbered address electrodes separately and therefore, there is a problem that power consumption is large. Further, the pulse applied to the address electrode is synchronized with the sustain pulse and, therefore, there is a problem that the dispersing effect of the discharge timing is insufficient.
Patent document 1: Japanese Unexamined Patent Publication (Kokai) No. 6-4039
Patent document 2: Japanese Unexamined Patent Publication (Kokai) No. 11-149274
Patent document 3: Japanese Unexamined Patent Publication (Kokai) No. 10-133622